The present invention relates to the headbox of a paper machine. More particularly, the invention relates to a headbox which comprises a stock distribution header part connected to an assembly of distribution pipes followed in the flow path of the stock suspension by an equalizing passage. The equalizing passage is most appropriately in immediate communication with an air tank. A turbulence section follows the equalizing passage and a converging slice part follows the turbulence section. The converging slice part has a lower lip wall and an adjustble upper lip wall.
U.S. Pat. No. 3,791,918 of the inventor discloses a headbox structure which comprises a stock distribution header and a distribution pipe assembly followed by a so-called middle chamber. This is followed further by a partitioned flow channel part and finally by a converging slice section. In the aforedescribed patent, the flow channel part comprises several parallel vanes, spaced apart and inclined with reference to the vertical direction, defining between themselves turbulence flow channels which have a cross-section of a parallelogram.
The headbox design disclosed in the aforedescribed patent has proved to be advantageous, but it has a disadvantage, which is the high cost of construction, particularly of the flow vane channel part. Another disadvantage is that the headbox has a fixed construction, so that it is impossible in paper machines which are provided with this type of headbox to vary substantially the grade of paper to be produced. It is also impossible to accurately adjust the headbox characteristics to correspond to the requirements of the stock type used or the paper quality to be produced.
In Finnish patent application Nos. 800018 and 801167 of the inventor, some headbox solutions utilizing cassette construction are described. The object of the solution is expressly that those parts which confine the flow channel in the headbox are exchangeable cassette-like sections, so that the headbox may be composed of replaceable components. It is thus relatively easy to change the headbox construction in case the type of production is changed. Such a structure also facilitates the cleaning of the interior of the headbox and its overall maintenance, compared with conventional constructions.
The features of the headbox of the invention are also applicable to headboxes for the production of multilayer paper grades. In this respect, reference is made, for example, to Finnish patent application No. 801587 of the inventor. This patent application discloses a headbox for a paper machine producing multilayer paper grades, in which headbox there are two or more separate flow channels for stock suspensions. The flow channels join in the slice region of the headbox, and each comprises a distribution header, a distribution pipe assembly part, or its equivalent, and further equalizing and turbulence sections for stock flow. One rigid grating plate member is provided between the flow equalizing section and the turbulence section. The rigid grating plate member is provided with several series of flow apertures. The turbulence section constitutes several parallel plate vanes, or their equivalent, fixed in position, principally at their front ends, in the grating plate part. One or more middle plates, extending right up to the slice region of the headbox, are provided between the horizontal series of plate vanes.